Comparison of extraction techniques for quantitative analysis of pendimethalin from soil and rice grain

Dissipation of Pendimethalin in Soil Under Direct Seeded and Transplanted Rice Field

The dissipation of pendimethalin applied in direct seeded rice (DSR) and transplanted rice (TPR) field at 1.0 and 2.0 kg a.i. ha^-1 followed biphasic first order kinetics (R² > 0.91) and was comparatively faster under flooded TPR than DSR. The half-life (DT₅₀) of pendimethalin in the soil ranged from 2.22 to 2.80 days in the initial phase and 23.51 to 24.66 days in the final phase in TPR for both application rates. However in DSR, DT₅₀ varied from 3.67 to 4.35 days in the initial phase and 34.19 to 34.99 days in the final phase. Residues of pendimethalin in soil samples analyzed by HPLC and GC-MS/MS were below the detection limit (< 0.003 µg g^-1) for both the application rates in DSR and TPR whereas 0.003-0.009 µg g^-1 and 0.003-0.008 µg g^-1 residues of pendimethalin were found in rice grain and straw samples, respectively.

Determination of pendimethalin in water, sediment, and Procambarus clarkii by high performance liquid chromatography-triple quadrupole mass spectrometry

We established a high-performance liquid chromatography-triple quadrupole mass spectrometry method for the analysis of pendimethalin residues in water, sediments, and Procambarus clarkii (Louisiana crayfish) tissues. Water samples were concentrated on a HLB solid-phase extraction column and eluted with dichloromethane and acetone (1:1). After drying under a stream of nitrogen gas, the sample volume was adjusted to 1 mL with the mobile phase solvent methanol/water/acetic acid (8:20:0.1). Pendimethalin was extracted with ethyl acetate containing 0.1% acetic acid, after rotary evaporation to dryness at 35 °C, the residue was dissolved in mobile phase solvent, purified by a neutral alumina column and graphitized carbon black powder (0.1 g). The mass characterization was conducted in positive ion mode, and the corresponding ions were detected in multi-reaction monitoring mode. The linear equations were y = 1 × 10⁶x + 14275, at pendimethalin levels of 0.05-20 μg L^-1 and y = 691029 × - 414368 for 20-200 μg L^-1. The detection limits of pendimethalin in water, sediments, and P. clarkii tissues were 1.0 × 10^-4μg L^-1 , 5.0 × 10^-3μg kg ^-1 and 5.0 × 10^-3 μg kg ^-1, respectively. The spiked recoveries ranged from 81.6 to 106.3%, and the relative standard deviations ranged from 4.58 to 13.6% (n = 6). The method provided an efficient and low-cost extraction and purification procedure that enabled a sensitive determination of pendimethalin in water as well as complex matrices.

Effect of repeated application of pendimethalin on its persistence and dissipation kinetics in soil under field and laboratory conditions

The repeated application of herbicide can alter its persistence in the environment. In India, wheat fields are exposed to herbicide application at least once in the cropping season. The present study investigated the dissipation behavior of pendimethalin applied annually to a wheat field over four cropping seasons from 2012 to 2016. The dissipation studies were also conducted under laboratory conditions during 2015-2016. Pendimethalin from soil and wheat grain samples was extracted using matrix solid-phase dispersion and quantified using high-performance liquid chromatography and gas chromatography-tandem mass spectrometry. The average recoveries of pendimethalin from soil and crop produce ranged from 81.3% to 103.1%. The half-life of pendimethalin ranged from 20.9 to 31.3 days and 9.4 to 60.2 days under field and laboratory conditions, respectively. Dissipation of pendimethalin varied significantly over the years under field conditions and was comparatively faster than under laboratory conditions. On the other hand, non-significant variation in the dissipation of pendimethalin in soils under laboratory conditions was observed. The residues of pendimethalin in crop produce at harvest were below the maximum residue limit set by EPA.